Any metallic structure which is positioned in an offshore salt water environment, will, after a period of time, be subjected to progressive corrosion and deterioration of exposed metallic parts. One way to prevent or at least deter such corrosive action is through the use of coatings such as paints and anti-corrosion systems which are capable of counteracting the deleterious effects. It has been found desirable for example to provide submerged parts of the structure with a series of sacrificial anodes. Thus, rather than the structure's metallic parts deteriorating under the cathodic effects of corrosive action, the sacrificial anodes will progressively deteriorate.
This method of corrosion control is widely practiced by the petroleum industry. Offshore drilling and producing structures frequently utilize sacrificial anodes in their prevention systems.
To monitor the degree of protection for the structure, these sacrificial anodes must be periodically surveyed. Normally, offshore structures are subjected to scheduled inspections usually by divers who descend with the necessary instrumentation to both test and observe the degree of protection afforded by the many sacrificial anodes. In relatively shallow water, the use of divers is practical and entails minimal expense. Notably, the water depth will be a primary expense factor.
The present generation of offshore structures of the type contemplated is often made for use in water depths on the order of magnitude of 1,000 feet and greater. It can be appreciated therefore that for such a structure, the use of divers to periodically descend and check the anti-corrosion system can be an expensive as well as a dangerous operation.
The prior art has dealt with the subject of cathodic protection and monitoring equipment therefor. U.S. Pat. No. 4,056,446, for example, teaches the use of an instrument package which is guidably raised and lowered through the steel members of an offshore structure to gather the necessary data. This arrangement, however, embodies limitations which restrict its utility. In U.S. Pat. No. 4,609,448, patented Sept. 2, 1986, an improved system is disclosed for readily monitoring a segment of an offshore submerged structure.
Toward simplifying the monitoring and inspection process for relatively tall or deep water structures, the present invention provides a further improved means whereby the cathodic protection system can be more accurately monitored. Further, it can be achieved without the use of divers and by a relatively simple apparatus incorporated into the structure.
The apparatus comprises primarily a package or combination of electronically sensitive monitoring instruments and ancillary equipment. The entire unit is capable of being raised and lowered on an instrument carriage which slides along guide cables. Cable means communicates the package with surface equipment to remotely record the obtained readings.
It is therefore an object of the invention to provide a cathodic protection monitor system for a structure positioned in an offshore body of water.
A further object is to provide a corrosion detecting monitor system which is operated and controlled from a structure's deck whereby to minimize or avoid the use of divers
A still further object is to provide a corrosion detection system including a mobile, instrument-carrying carriage that will not interfere with accurate electronic readings.